H2 Biology 18 - Mitosis

controlled by G1, G2, M checkpoints; determine if cell cycle can proceed >

req of each checkpoint must be met b4 cells -> next stage(DNA repn is accurate/bring about DNA repair mechanisms if req) >

prevent dysregulation of checkpoints of cell division, prevents excessive CCP & UCD which leads to TF & possibly cancer >

tight control needed for normal cell division, cell development OR prevent cells w/ damaged DNA from continuing cell cycle

P

chromatin condenses, form chromosomes >

2 pairs of centrioles move opp poles of cell, SFs formed >

NE disintegrates, fragments into NM vesicles

M

2 pairs of centrioles positioned @ opp poles of cell >

KSFs pull on centromeres, arrange chromosomes in single row on M plate

A

SF attached to centromere shorten & contract, pulls SCs to opp poles of cell >

centromeres divide, SCs separate @ centromere >

each SC becomes DC

T

DC pulled by SF attached to centromere reach opp poles of cell >

chromosomes uncoil, lengthen & become indistinct to form chromatin again >

SFs disintegrate >

NM vesicles bind to chromosomes & fuse tgt, NE reforms around chromatin in daughter cell

Interphase(G1,S,G2 checkpoints)

longest phase of cell cycle, period of intense synthesis of cellular materials, growth >

nucleic acids, proteins, carbohydrates synthesised for own growth >

SCDR occurs @ S phase, amount of DNA x2, chromosome no. same >

each chromosome consists 2 genetically identical SCs held tgt @ centromere >

each SC exact copy of chromosome before replication >

chromatin remains uncoiled, decondensed

Mitosis

replicated copies of each chromosome, associated proteins precisely divided, enclosed into 2 daughter nuclei in PMAT

Cytokinesis

furrow develops in animal cell/cell plate formation in plant cell; division of cytoplasmic content, produce 2 genetically identical daughter cells

growth

enables multicellular organism grow, develop from 1 single cell;fertilised egg >

if tissue must enlarge in growth, new cells must be genetically identical to existing cells; new cell reproduction achieved by mitosis

repair

after organism fully-grown, cell division continues to function in renewal, repair of tissues >

damaged, worn-out cells replaced by exact copies to return tissue to former condition; achieved via mitosis

asexual reproduction

production of new individuals of species by 1 parent organism >

most organisms propagated by AR, results in clones so that species can colonise particular stable, well-adapted habitat within shortest time period

SCDR occurs during S phase of interphase, form SCs genetically identical to parent DNA >

during M each chromosome arranged on M plate; each SC of chromosome face opp poles of cell >

separation of SCs during A lead to formation of genetically identical DC, ensures even distribution of DC into daughter nuclei; forms 2 genetically identical nuclei in daughter cells >

no crossing over/exchange of segments b/w non-SCs of HCs; no genetic recombination/variation >

ensures production of genetically identical cells

SCDR occurs, S phase of interphase, produce 2 identical DNA molecules >

each chromosome consists 2 identical SCs held tgt @ centromere >

@ start of mitosis, chromosome exists uncoiled, decondensed chromatin >

DNA molecule wind around histone octamer -> nucleosome >

nucleosomes connected by linker DNA, associates w/ H1 histones -> nucleohistone complex >

H1 histone interaction results in further coiling into 30nm chromatin fibre >

30nm chromatin fibre forms looped domains attached to scaffolding proteins

-> 300nm chromatin fibre >

centromere is constricted region on chromosome made up of non-coding DNA of series of tandem repeat seq >

no. of centromere-associated proteins bind to centromeric DNA -> kinetochore

hold SCs tgt, divide allowing separation of SCs into DC >

centromeric DNA essential for proper alignment, separation of SCs/HCs to opp poles of cell during nuclear division >

ensure proper segregation of chromosomes by being site on chromosome where kinetochore assembles, SFs from centrioles attach during nuclear division >

consists of specific non-coding DNA made up of series of tandem repeat seq which no. of centromere-associated proteins bind, forms kinetochore

act as MTOC in nuclear division >

2 pairs of centrioles move to opp poles of cell, determines polarity of cell >

centrioles produce SFs @ poles towards equator of cell, organise synthesis of SFs, leads to separation of chromatids during cell division

guide movement of chromosomes during nuclear division; align chromosomes @ M plate, move chromatids/chromosomes to opp poles of cell during anaphase >

ensure each daughter cell receives exact no. of chromosomes during cell division